Portable medication delivery devices are generally known for the administration of a medicinal fluid or drug that is suitable for the self-administration by a patient. A drug injection device is especially useful in the shape of a pen, which can be handled easily and kept everywhere available. A sophisticated type of drug delivery device is constructed to be refillable and reusable many times. A dose of a drug is delivered by means of a drive mechanism, which also allows to set the amount of fluid to be thus injected.
DE 102 37 258 B4 describes a drug delivery device in the shape of an injection pen having a drive mechanism, which allows to deliver a plurality of different prescribed doses. The drive mechanism comprises rotatable elements, which are rotated relatively to one another around a common axis and are coupled by a gear that is arranged between opposite faces of the rotatable elements. The gear comprises a modified ratchet formed by sequences of corresponding ramps sloping in azimuthal direction along the rims of the opposite faces of the rotatable elements. The slope of each ramp is followed by a steep flank, thus rendering a sawtooth shape of the gear, which is apparent when the rotatable elements are viewed during rotation in a radial direction towards the axis.